Detection of fast-neural signal using depth-resolved spectroscopy via intensity modulated interferometry having tunable pump laser

Abstract

An optical measurement system and method are provided. Pump sample light and probe sample light are delivered through into an anatomical structure of a user. The anatomical structure has molecules having a resonant vibrational frequency equal to the difference between a first optical frequency of the pump sample light and a second optical frequency of the probe sample light, whereby a portion of the probe sample light is inelastically scattered by the molecules as signal light encoded with a physiological event occurring in the molecules, and whereby sample light comprising the signal light exits the anatomical structure. Signal light in the exiting sample light is detected, and an electrical signal representative of the signal light is outputted. The electrical signal is analyzed, and based on this analysis, the presence and the depth of the physiological event in the anatomical structure is determined.

What is claimed is: 
     
       1. An optical measurement system, comprising:
 a pump optical source configured for generating pump source light having a first optical frequency; 
 a probe optical source configured for sequentially generating probe source light over a range of second optical frequencies; 
 an optical modulator configured for intensity modulating the pump source light at a modulation frequency; 
 an interferometer configured for:
 splitting the intensity modulated probe source light into probe sample light and probe reference light; 
 delivering the intensity modulated pump source light as intensity modulated pump sample light, and the probe sample light, into an anatomical structure comprising molecules having a resonant vibrational frequency equal to the difference between the first optical frequency and one of the range of second optical frequencies, whereby a portion of the probe sample light is inelastically scattered by the molecules as signal light intensity modulated at the modulation frequency and encoded with a physiological event occurring in the molecules, a portion of the probe sample light is elastically scattered by the anatomical structure as non-modulated background light, and a portion of the pump sample light is scattered by the anatomical structure as intensity-modulated background light at the modulation frequency, and whereby sample light comprising the intensity modulated signal light, the non-modulated background light, and the intensity-modulated background light exits the anatomical structure; 
 filtering the intensity-modulated background light from the exiting sample light; and 
 combining the intensity modulated signal light and non-modulated background light of the filtered sample light and the reference light into interference light having a first plurality of frequency components and a second plurality of frequency components displaced from the first plurality of frequency components, each of the first plurality of frequency components being encoded with a physiological event at a different depth of the anatomical structure; 
 
 an optical detector configured for detecting the interference light and outputting an electrical signal comprising the first plurality of frequency components; and 
 a processor configured for analyzing the first plurality of frequency components in the electrical signal, and, based on this analysis, determining a presence and a depth of the physiological event in the anatomical structure. 
 
     
     
       2. The optical measurement system of  claim 1 , wherein each of the pump source light and the probe source light is continuous wave (CW) light. 
     
     
       3. The optical measurement system of  claim 1 , wherein the probe optical source has a coherence length equal to or less than 1 cm. 
     
     
       4. The optical measurement system of  claim 1 , wherein the anatomical structure is a brain. 
     
     
       5. The optical measurement system of  claim 4 , wherein the physiological event is indicative of neural activity. 
     
     
       6. The optical measurement system of  claim 5 , wherein the physiological event is a fast-neural signal. 
     
     
       7. The optical measurement system of  claim 6 , wherein the molecules are neural membrane proteins. 
     
     
       8. The optical measurement system of  claim 1 , wherein the probe optical source is configured for sequentially generating the probe source light over a range of second optical frequencies by sweeping the probe source light over the range of second optical frequencies. 
     
     
       9. The optical measurement system of  claim 1 , wherein the range of second optical frequencies has a width less than a bandwidth of a Raman band of the molecules. 
     
     
       10. The optical measurement system of  claim 9 , wherein a difference between the first optical frequency and a central optical frequency of the range of second optical frequencies coincides with a center of the Raman band of the molecules. 
     
     
       11. The optical measurement system of  claim 1 , wherein the pump optical source is a tunable optical source. 
     
     
       12. The optical measurement system of  claim 1 , wherein the electrical signal comprises the first plurality of frequency components and the second plurality of frequency components, the optical measurement system further comprising a filter configured for filtering the second plurality of frequency components from the electrical signal. 
     
     
       13. The optical measurement system of  claim 1 , further comprising an oscillator configured for generating an oscillating signal at the modulation frequency, wherein the modulator is configured for intensity modulating the pump source light in response to the oscillating signal. 
     
     
       14. The optical measurement system of  claim 1 , further comprising an optical beam combiner configured for combining the pump sample light and the probe sample light, wherein the interferometer is configured for delivering the combined pump sample light and probe sample light into the anatomical structure at a single location. 
     
     
       15. The optical measurement system of  claim 1 , wherein the interferometer is configured for respectively delivering the pump sample light and the probe sample light into the anatomical structure at different locations. 
     
     
       16. The optical measurement system of  claim 1 , wherein the optical detector comprises a balanced detector. 
     
     
       17. The optical measurement system of  claim 1 , wherein the interference light comprises a speckle interference pattern having a plurality of speckle grains, and wherein the optical detector comprises a camera having an array of pixels configured for respectively detecting the speckle grains. 
     
     
       18. The optical measurement system of  claim 1 , wherein the optical detector is configured for simultaneously detecting the first plurality of frequency components in the interference light. 
     
     
       19. The optical measurement system of  claim 18 , wherein the processor is configured for transforming the electrical signal from a time domain into a frequency domain, and analyzing the electrical signal in the frequency domain, and based on this analysis, determining the presence and depth of the physiological event in the anatomical structure. 
     
     
       20. The optical measurement system of  claim 1 , wherein the optical detector is configured for sequentially detecting the first plurality of frequency components in the interference light, and wherein the processor is configured for analyzing the electrical signal in the time domain, and based on this analysis, determining the presence and depth of the physiological event in the anatomical structure. 
     
     
       21. The optical measurement system of  claim 20 , wherein the optical detector is a conventional camera, and the optical measurement system further comprises:
 an optical modulator configured for intensity modulating the pump source light at a modulation frequency to create the pump sample light; and 
 a controller that sequentially varies the modulation frequency, such that wherein multiple ones of the first plurality of frequency components are sequentially detected by the conventional camera. 
 
     
     
       22. The optical measurement system of  claim 20 , wherein the camera is a lock-in camera configured for sequentially locking into multiple ones of the first plurality of frequency components in the interference light. 
     
     
       23. The optical measurement system of  claim 1 , wherein the exiting sample light comprises multiple optical modes. 
     
     
       24. The optical measurement system of  claim 1 , wherein the interferometer comprises a beam splitter configured for splitting the probe source light into the probe sample light and the probe reference light, and an optical beam combiner configured for combining the signal light of the exiting sample light and the reference light into the interference light. 
     
     
       25. The optical measurement system of  claim 1 , wherein the processor is configured for determining the presence and depth of the physiological event in the anatomical structure by comparing the first plurality of frequency components in the electrical signal to a plurality of reference frequency components. 
     
     
       26. The optical measurement system of  claim 1 , wherein the pump optical source comprises a pump laser, and the probe optical source comprises a probe laser.